wow, that smells like a logic bug to me. If not, then the documentation needs a VERY obvious warning about how to properly do mirrored devices with mirrored logs (nee 4+ distinct PV devices). If the internals can't be fixed, then it needs to error out on creation when there aren't 4 devices to work with. Any particular reason why you wanted pseudo-external logs in the first place?

Does 'lvcreate -nv' show you the work plan?

Yet lvconvert looks the right tool for me if I could overcome this limitation. I guess you meant 'lvconvert' instead of 'lvcreate' because lvcreate works fine and I don't think it needs to be debugged. The only drawback is that I need a much more complicated migration.

In case you needed the "lvconvert" here it is (pretty long) the output of